Stainless steel was first recognized as a commercial proposition in 1913, by Harry Brearley, a metallurgist in Sheffield, England, after he noticed that certain gun barrels containing around 13% chromium didn’t rust when they were left outside. What he’d discovered was a steel that approximates to what we know today as type 420 stainless, a grade used to make table knives. Commercial production of this material didn’t start until after the first world war, by which time Doctors Strauss and Maurer at Krupp in Germany were busy discovering what we know as the 18-8 stainless steels. Britain started production of these steels in 1923, under license from the Krupp patent.

This represented the beginnings of stainless steel production and the first steps in a long fight against the many corrosive media which were lurking around to eat up anything that was a piece of steel.

The corrosion resistance of stainless steels is due to the presence of an extremely thin protective oxide film, the so-called “passive film” which forms spontaneously on the steel surface when it’s exposed to air or some other gas or liquid which can supply oxygen to the steel surface. In fact, stainless steel is like humans, in that it needs oxygen to survive. This film is transparent and tightly adherent to the steel, and is so thin, probably less than 0.000001” thick, that it is absolutely invisible while in contact with the surface it’s formed on. The film is insoluble in water and in many other liquids, and impermeable to these and to many gasses.  While it remains intact and tightly adherent to the steel surface, there will be protection from corrosive attack. It seems strange that a huge, heavy weight stainless steel forging owes its corrosion durability to a microscopically thin film, but that’s the way it is. And even if the film is broken locally, serious corrosion will not result providing oxygen is present because the film spontaneously repairs.  If the ruptured film is prevented from repairing itself, corrosion of the steel will continue and will result in either pitting or general attack over the steel’s surface. The protective value of the oxide film on stainless steel will increase with its chromium content. If the steel contains significant amounts of other metals such as nickel or molybdenum, the oxides of these metals will also be present in the film and will improve its resistance to certain types of corrosive attack.

Look for additional blogs on this subject within steelforge.com.  All Metals & Forge Group is a manufacturer of stainless steel forgings and seamless rolled rings for industrial uses, including the PH grades.  This allows AMFG to manufacture the widest range of forged shapes for use in the Industries Served listed on steelforge.com.

by Royce Lowe

In 2022, wind energy increased by some 265 TWh, or 14%, to reach over 2100 TWh. This represented the second highest growth among renewable power technologies, behind solar PV.  

But to make serious progress towards the Net Zero Emissions by 2050, which is looking to approximately 7,400 TWh of wind electricity generation in 2030, the average annual generation growth rate needs to increase to about 17%. Thus wind capacity will continue to grow, along with all the hardware that goes along with it.

Most wind farms, some 90 percent, are situated onshore. Unlike offshore farms, they are not susceptible to the effects of seawater spray, but they may be attacked by pollution, rain, dust particles, or other environmental or operational stresses. It has been so far proven that for certain components of a wind turbine the use of stainless steel is advantageous. In addition to its corrosion resistance, the alloy can be easily formed and welded, and in most cases easily machined. It is available as forged parts, and as sheet and plate and rounds. It has excellent toughness at ambient and sub-zero temperatures.

Offshore wind farms are surrounded by seawater, thus subject to constant exposure to salt spray. This means that stainless steel is relied upon in many applications, such as fasteners, safety cables, davit cranes, and fittings. The use of stainless steel in both onshore and offshore wind farms greatly extends the lifetime of wind turbines, and minimizes required maintenance. Stainless steel is relatively easy to clean.

Type 304/304L stainless steel might be described as the workhorse of this group of versatile alloys. 

Type 304L, to which most 304 grades are currently manufactured, is made to 0.03% carbon, and if extra strength is required then nitrogen is added. Type 304L is not susceptible to carbide precipitation during service or welding, hence requires no special precautions, as does type 304. Its basic chemistry is 18.0 to 20.0% chromium and 8.0 to 12.0% nickel. Type 304L has good corrosion resistance in moderately reducing or moderately oxidizing environments. As such, this alloy will be resistant to the elements of rain and all the “foreign bodies” that might be floating around in its environment, hence, its suitability for onshore wind turbine parts. Type 304 cannot be hardened by heat treatment, solely by cold working the material.

Stainless grades 15-5PH and 17-4PH are stainless precipitation-hardening steels that show corrosion resistance similar to that of type 304L. The steels show good forgeability, and unlike the austenitic 304 type, these steels may be hardened by solution treatment followed by a low-temperature hardening. Machinability is good, providing the correct hardening temperature is chosen.

Here are the  chemical analyses of these two steels: 

These two precipitation hardening alloys show good strength and machinability. They may be heat treated to a whole range of mechanical properties by control of the hardening temperature following solution annealing.

When operating in more corrosive areas, as in offshore, it requires a material that will better withstand attack from salt water. Although salt water might be said to be nature’s most corrosive medium, in the case of wind turbines it happens mostly in the form of spray. Immersion of steel, any steel, in salt water, will result in destruction. Exposure to spray is less serious, particularly if the steel can be periodically cleaned. It is likely that the turbine components in stainless steel will be hidden, thus partly protected.

Type 316 stainless steel has much better corrosion resistance than the three grades previously mentioned. Its chemical analysis is: carbon – 0.08% max; chromium – 16.0/18.0%; nickel – 10.0/14.0%; molybdenum – 2.0/3.0%. The alloy is often melted to 0.03% carbon, as with 304L, to prevent carbide precipitation during welding or service. It is the molybdenum in type 316 that gives it the added corrosion resistance, as it reduces pitting of the surface during exposure to the chloride ion in seawater. Frequent cleaning during service, where possible, will help to reduce attack.

 On both land and sea, stainless steels, well-chosen and well fabricated, treated and maintained, will give years of service in the generation of electricity.

by Royce Lowe

The United States has always been one of the world leaders in the oil and natural gas business. Still, with the intensity of fracking a couple of decades ago, it became the world’s number one producer of crude oil and natural gas. Fracking, or hydraulic fracturing, is a technique for recovering gas and natural oil from shale rock. Put simply, it involves drilling into the earth and directing a high-pressure mixture of water, sand, and chemicals at a rock layer to release the natural gas inside. A few years ago, it was estimated that of a million or so oil and natural gas wells in the United States, around 70% were drilled and fracked. 

Another business that goes along with fracking is that of making, shaping, and treating the steel and other metals used to fabricate the drill collars, gears, valve bodies, and fracture pumps. There’s an awful lot of liquid involved in a fracking operation, with millions of gallons of water as the major constituent of the liquid feed, topped up by fracking chemicals and what are called proppants, a sand constituent that is there to keep open the fracking cracks formed from initial drilling.  The oil and gas industry is one of the largest consumers of specialty pipe and tube products. These products are used in various applications, such as drilling, production, and oil and gas transportation. 

The steel components used in the overall fracking infrastructure must be strong and resistant to the numerous thuds and shocks they’ll undergo during the drilling, extraction, and storage operations, as well as the abrasion from all the sand floating around. So, which grades of steel are recommended for use in the oil and gas industry?

Grades 4130, 4140, and 4340 are up to the task or performing well in this harsh environment. These are low alloy steels that may be heat treated to the required mechanical properties for their operating environment. They may be easily machined, particularly if heat treated to the spheroidized annealed condition. They are easily welded but should be treated with care. The three grades complement each other as applied to the oil and gas industry. This is the basic chemistry of the respective alloy steels: 

We will note from the carbon contents that type 4140, for a given heat treatment procedure, will 

produce a harder, stronger material than type 4130. Type 4340, a nickel-bearing steel, will produce the strongest material of the three. It will also hold its strength to around 600 degrees Fahrenheit. It is tough and will hold its toughness to sub-zero temperatures. The hardenability of type 4340 – the ability to be hardened to depth within the steel – is far greater than that of both 4140 and 4130.

Forged components are indispensable in the oil and gas industry thanks to their ability to withstand high pressure, low temperature, and corrosive environments. Key applications include forged flanges that provide secure and leak-proof connections in pipelines, valves, and pressure vessels. Pipelines for transportation would typically be made from 4130 grade, a somewhat less expensive material than 4340 but suitable for the application.

Forged components in the grades listed above will require heat treatment to specified strength and toughness levels. This requires detailed knowledge, garnered over years of experience, of the specific treatments required to obtain desired properties. The treatments may be annealing for optimum machinability or hardening and tempering to give the required strength and toughness levels. 

In the event that the forged parts may exhibit non-uniform deformation throughout a part – because of a complicated shape – a normalizing treatment will be called for prior to undertaking hardening and tempering. It should be noted that the knowledge and experience of the people responsible for heat treatment are a very important part of this operation, as are those responsible for the forging, where forging temperatures and proper reductions come largely from past experience.

The three grades noted above, 4130, 4140 and 4340, will combine to form the necessary infrastructure for a fracking well. The cost of 4340 material will be significantly higher than that of the other two grades. These three steels, forged, heat treated, machined and welded, will all do their part in bringing oil and natural gas to industry and homes.

All Metals & Forge Group stocks raw material in these grades, so it can provide rough machined forgings in 8 to 10 weeks to fulfill your order. Contact one of our Forging Specialists at (973) 276-5000 or sales@steelforge.com.